1. Technical Field
The present invention relates to a high-frequency signal transmission line, more specifically to a transmission line having variable characteristic impedance and a combiner for combining a plurality of filters using the same.
2. Background Art
RF signal transmitters used for mobile communication base stations divide the output signal into a plurality of identical signals, amplify the divided signals and recombine these signals, in order to increase the transmission output.
A base station transceiver of a mobile communication system is constituted with a splitter for splitting an inputted RF signal such as a subscriber signal, a power amplifier for high-power-amplifying each of the RF signals split by the splitter, and a combiner for combining the RF signals amplified by the power amplifier.
In the conventional base station base station transceiver, the power amplifier high-power-amplifies each of the RF signals split by the splitter, and then the RF signals high-power-amplified by the power amplifier are combined and outputted through the combiner.
The combiner uses simple power distribution and combining technologies, and thus shows a good signal combining property only when RF signals having identical signal characteristics, i.e., identical amplitude, identical time delay and identical phase, are inputted. When the signal characteristics are different from one another, the combining property is degraded, and reflected wave signals are inputted to the power amplifier.
The frequency band provided to mobile communication services can be constituted with a plurality of non-contiguous sub-frequency bands. Accordingly, a plurality of band pass filters (BPF) are used to filter out frequency bands that are not used for the services, and signals that have passed through the plurality of BPFs are combined to a single signal and transmitted through the combiner.
As various bands of frequencies, ranging from a few hundred MHz to a few GHz, are used in mobile communication services, problems caused by different signal characteristics can occur when various output signals that have passed through the plurality of BPFs are combined to and transmitted as a single signal.